If $x \star y = 7x+y$ and $x \triangleleft y = 4x-y$, find $(3 \triangleleft 6) \star -3$.
Explanation: First, find $3 \triangleleft 6$ $ 3 \triangleleft 6 = (4)(3)-6$ $ \hphantom{3 \triangleleft 6} = 6$ Now, find $6 \star -3$ $ 6 \star -3 = (7)(6)-3$ $ \hphantom{6 \star -3} = 39$.